Image display devices are being widely used in a variety of applications, including TV screens, monitors of personal computers, etc. The plasma display panel (PDP) is gaining popularity as a next-generation display device to replace the CRT because a PDP is thin and a large screen can be readily fabricated with a plurality of units. A PDP includes a plasma display panel on which an image is displayed using a gas discharge phenomenon, and exhibits superior display capabilities, including high display capacity, high brightness, high contrast, clear latent image, a wide viewing angle, etc. In a PDP apparatus, when a direct current (DC) or alternating current (AC) voltage is applied to electrodes, a discharge of gas plasma is created, resulting in the emission of ultraviolet (UV) light. The UV emission excites adjacent phosphor materials, resulting in electromagnetic emission of visible light. Despite the above advantages, PDPs face several challenges associated with driving characteristics, including an increase in electromagnetic wave radiation, near-infrared emission, and phosphor surface reflection, and an obscured color purity due to orange light emitted from helium (He), neon, or xenon (Xe) used as a sealing gas.
Some believe that the electromagnetic waves and near-infrared rays generated in PDPs may adversely affect human bodies and cause malfunctions of precision machines such as wireless telephones or remote controllers (e.g., see US 2006/0083938, incorporated herein by reference). These waves, taken individually or collectively, may be referred to as electromagnetic interference (EMI). Thus, in order to make use of such PDPs, there is a desire to reduce the electromagnetic waves and near-infrared (IR or NIR) rays emitted from the PDPs to a predetermined level or less. In this respect, various PDP filters have been proposed for shielding electromagnetic waves or near-infrared rays emitted from the PDPs, reducing reflection of light and/or enhancing color purity. The proposed PDP filters are also required to meet transmittance requirements because the filters are installed on a front surface of each of the PDPs.
In order to reduce the electromagnetic waves and NIR waves emitted from plasma display panels to a predetermined level or less, various PDP filters have been used for the purposes of e.g., shielding electromagnetic waves or NIR emitted from the PDPs, reducing reflection of light and/or enhancing color purity. High transmittance is required for such filters because they are generally applied to the front surface of PDPs. Typical electromagnetic wave shielding filters meeting such requirements and characteristics are classified into a metal mesh-pattern filter and a transparent conductive film filter. Although the metal mesh-pattern filter exhibits a good electromagnetic wave shielding effect, it has several disadvantages including poor transmittance, image distortion, and an increase in the production cost due to a costly mesh. Due to such disadvantages, electromagnetic wave shielding filters using transparent conductive films using indium tin oxide (ITO) are being widely used instead of the metal mesh-pattern filter. The transparent conductive film is generally formed of a multi-level thin film structure in which a metal film and a high-refractive-index transparent thin layer are sandwiched. Silver or a silver-based alloy may be used as the metal film. However, convention PDP EMI filters tend to lack durability and/or can stand to be improved upon with respect to visible transmission and/or shielding properties.
Moreover, certain PDP EMI filters need to be heat treated (e.g., thermally tempered). Such heat treatment typically requires use of temperature(s) of at least 580 degrees C., more preferably of at least about 600 degrees C. and still more preferably of at least 620 degrees C. The terms “heat treatment” and “heat treating” as used herein mean heating the article to a temperature sufficient to achieve thermal tempering and/or heat strengthening of the glass inclusive article. This definition includes, for example, heating a coated article in an oven or furnace at a temperature of least about 580 degrees C., more preferably at least about 600 degrees C., for a sufficient period to allow tempering and/or heat strengthening. In certain instances, the HT may be for at least about 4 or 5 minutes. The use of such high temperatures (e.g., for 5-10 minutes or more) often causes coatings to break down and/or causes one or more of the aforesaid desirable characteristics to significantly deteriorate in an undesirable manner. Conventional PDP EMI filters tend to suffer from a lack of thermal stability and/or durability upon heat treatment (HT). In particular, heat treatment tends to cause conventional PDP filters to break down.
In view of the above, there exists a need in the art for an improved PDP filter which is improved (with respect to conventional PDP EMI filters) with respect to one or more of: (i) improved chemical durability, (ii) improved thermal stability (e.g., upon optional heat treatment such as tempering), (iii) improved visible transmission, and/or (iv) improved EMI shielding properties.